The present application is based on and claims priority from Japanese Patent Application 2000-238627, filed Aug. 7, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a voltage regulator of a vehicle AC generator and, particularly. a voltage regulator having a semiconductor switch element for controlling field current to be supplied to a field coil of a vehicle AC generator.
2. Description of the Related Art
A recent voltage regulator of a vehicle AC generator is provided with various electronic circuits, such as a comparator, an operational amplifier, an oscillating circuit and/or the like, disposed in an IC chip. A constant voltage power circuit is also provided in order to supply constant voltage power to such circuits.
On the other hand, a number of electro-magnetic actuators have been mounted in a vehicle. If two or more electro-magnetic actuators are turned off concurrently, a large negative surge voltage, such as shown in FIG. 7, is generated in a power line connected to a battery, and the negative surge voltage may be applied to a high-side terminal of the constant voltage circuit. In such a case, the output voltage, i.e. VDD, widely fluctuates, resulting in that the comparator and the oscillator can not operate properly.
Therefore, a main object of the invention is to provide an improved voltage regulator that is free from the above stated problems.
According to a main feature of the invention a voltage regulator of a vehicle AC generator includes a switching element connected between a battery and a field coil, a control circuit for controlling the switching element according to terminal voltage of the battery, a power circuit for providing a constant voltage from power supplied thereto and supplying the control circuit with the constant voltage and a reverse-current blocking diode having an anode connected through an outside power line to the battery and a cathode connected to the power circuit. Even if a large negative surge voltage is generated in a power line connected to a battery and applied to the power circuit, the output voltage, i.e. VDD, does not widely fluctuate, so that devices included in the voltage regulator, such as a comparator or an oscillator, can operate properly.
Preferably, a portion of the control circuit, the power circuit and the reverse-current blocking diode are integrated into an IC chip and separated by insulation layers. However, the reverse-current blocking diode may be formed at a portion separate from the IC chip. The IC chip and the portion at which the reverse-current blocking diode is formed may be disposed in a hybrid IC unit.
It is also preferable that the reverse-current blocking diode is fixed to a first conductive support plate and the power circuit is fixed to a second conductive support plate, and that
the first and second conductive support plates are thermally and electrically insulated from each other.
Further, each of the first and second support plates may be comprised of one of leads of a lead frame, the reverse-current blocking diode may have a cathode electrode connected to the power circuit by a bonding wire, and the reverse-current blocking diode, the power circuit and the bonding wires are molded together with resin.